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The electron-phonon interaction is known as one of the major mechanisms determining electrical and thermal properties. In particular, it alters the carrier transport behaviors and sets fundamental limits to carrier mobility. Establishing how electrons interact with phonons and the resulting impact on the carrier transport property is significant for the development of high-efficiency electronic devices. Here, carrier transport behavior mediated by the electron-phonon coupling in BiFeO3 epitaxial thin films is directly observed. Acoustic phonons are generated by the inverse piezoelectric effect and coupled with photocarriers. Via the electron-phonon coupling, doughnut shape carrier distribution has been observed due to the coupling between hot carriers and phonons. The hot carrier quasi-ballistic transport length can reach 340 nm within 1 ps. The results suggest an effective approach to investigating the effects of electron-phonon interactions with temporal and spatial resolutions, which is of great importance for designing and improving electronic devices.

Acoustically actuated magnetoelectric (ME) antennas based on resonant magnetoelectric coupling within ferromagnetic/piezoelectric ME laminated composites have recently been considered as a promising solution for antenna miniaturization. However, its radiation performance has been theoretically overestimated, since the negative effects on performances due to the magnetization saturation and the nonlinear mechanical behavior that occur from high-field driving have not been paid enough attention. This work presents a unique equivalent-circuit-based numerical method to analyze the near-field resonance radiation performances of ME antennas driven by high electric fields. In this method, we establish an equivalent circuit of the converse magnetoelectric effect for a ME laminated composite to describe the operating principle of acoustically actuated electromagnetic radiation. The equivalent parameters related to resonance characteristics are determined by fitting the circuit model to the data from frequency response measurements of the near-field magnetic flux density. The validity of the model is verified by comparing the theoretical predictions with the experimental results, in the view of the volume fraction dependence of the mechanical resonance-related radiation characteristics of the fabricated ME composites. Based on the proposed model, the influence of driving voltage amplitude on near-field radiation performances is further analyzed by experimental fitting to the model, and the potential limiting factors of ME antennas are discussed according to the driving-amplitude dependence of parameters obtained from the fit. This work provides an effective and engineering-friendly approach to predict the evolution of ME antenna performances, leading a way to improve the performance limit for resonant magnetoelectric coupling. [ABSTRACT FROM AUTHOR]

The micro-discharge effect limits the development of high-frequency microwave power components to miniaturization and integration. Therefore, it has become a focus of research to effectively suppress the micro-discharge effect, increase the micro-discharge threshold, and strengthen the environmental stability of high-frequency microwave devices. In this study, different elemental ratios of carbon (C)/silver (Ag)/titanium (Ti) composite films were obtained by multi-target magnetron co-sputtering technology and then systematically analyzed for micro-discharge effects. When the doping ratio of C/Ag/Ti was 3.538/1/0.013, the corresponding maximum secondary electron emission coefficient (δmax) decreased to 1.01 owing to the suppression of secondary electron emission by the increase in the content of sp2 hybrid bond. The micro-discharge threshold of Ku band waveguide filters coated with moderate C/Ag/Ti composite films showed an optimal performance of 10 000−12 500 W, which was increased by approximately 20 times. Moreover, the microstructure of the composite films exhibited higher density and flatness with a tiny increase in the titanium doping ratio, representing good environmental stability. Thus, the effective suppression of the secondary electron emission yield, significant improvement in the micro-discharge threshold, and enhancement of the environment stability of microwave components could be realized simultaneously by reasonably controlling the content of titanium in silver and titanium co-doped carbon-based composite films. [ABSTRACT FROM AUTHOR]

Controlling magnetization dynamics is imperative for developing ultrafast spintronics and tunable microwave devices. However, the previous research has demonstrated limited electric-field modulation of the effective magnetic damping, a parameter that governs the magnetization dynamics. Here, we propose an approach to manipulate the damping by using the large damping enhancement induced by the two-magnon scattering and a nonlocal spin relaxation process in which spin currents are resonantly transported from antiferromagnetic domains to ferromagnetic matrix in a mixed-phased metallic alloy FeRh. This damping enhancement in FeRh is sensitive to its fraction of antiferromagnetic and ferromagnetic phases, which can be dynamically tuned by electric fields through a strain-mediated magnetoelectric coupling. In a heterostructure of FeRh and piezoelectric PMN-PT, we demonstrated a more than 120% modulation of the effective damping by electric fields during the antiferromagnetic-to-ferromagnetic phase transition. Our results demonstrate an efficient approach to controlling the magnetization dynamics, thus enabling low-power tunable electronics.

For the application of high-frequency current detection in power systems, such as very fast transient current, lightning current, partial discharge pulse current, etc., current sensors with a quick response are indispensable. Here, we propose a high-frequency magnetoelectric current sensor, which consists of a PZT piezoelectric ceramic and Metglas amorphous alloy. The proposed sensor is designed to work under d15 thickness-shear mode, with the resonant frequency around 1.029 MHz. Furthermore, the proposed sensor is fabricated as a high-frequency magnetoelectric current sensor. A comparative experiment is carried out between the tunnel magnetoresistance sensor and the magnetoelectric sensor, in the aspect of high-frequency current detection up to 3 MHz. Our experimental results demonstrate that the d15 thickness-shear mode magnetoelectric sensor has great potential for high-frequency current detection in smart grids. [ABSTRACT FROM AUTHOR]

Half-metallic NiCo2O4 with high spin polarizability has great potential applications in spintronics. The manipulation of magnetic anisotropy is crucial for spintronics based on spin-transfer or spin–orbit torques, as it is directly related to the critical switching current density. Here, we report epitaxial growth of metallic NiCo2O4 film with perpendicular magnetic anisotropy on MgAl2O4 single crystal substrates. The modulation of the magnetic anisotropy was achieved by changing the growth conditions (deposition temperature and thickness) of NiCo2O4 films and by means of protonation. Strong dependence of magnetic coercivity on deposition temperature (350–500 °C) has been observed due to variable phase configuration. Furthermore, the magnetic coercive field can also be effectively controlled by the film thickness (3–78 nm) through strain relaxation. More importantly, spin reorientation transition has been achieved by proton and electron doping in the NiCo2O4 films, resulting in reconfigured valence states of Ni and Co cations and a magnetic easy axis rotation from out-of-plane to in-plane. The effective modulation of the magnetic anisotropy provides important insights into the functional design of NiCo2O4-based spintronics with ultralow energy dissipation. [ABSTRACT FROM AUTHOR]

Flexible electronics strongly demand the integration of flexible and large‐scale multifunctional oxides. BiFeO3 is one of the most essential multifunctional oxides that could be used in memories, logics, sensors, and actuators. Recently, freestanding single‐crystalline BiFeO3 membranes exhibited superior elasticity and flexibility. However, fabrication and integration of large‐scale freestanding BiFeO3 membranes into flexible electronics remain elusive. In this study, inch‐scale freestanding single‐crystalline BiFeO3 membranes are fabricated with assistance from a water‐soluble sacrificial layer. To transfer flat and crack‐free membranes, all the existing methods are first followed but fail. Then the study introduces a temporary supporting Cu layer on the surface of the as‐grown SiTiO3/Sr3Al2O6/(SrRuO3/)BiFeO3 heterostructure and successfully obtains full and crack‐free 5 mm × 5 mm freestanding membranes on various substrates. The residual strain within the heterostructure releases gradually under the protection of the Cu layer. The freestanding BiFeO3 membranes are relatively uniform among different regions and exhibit good dielectric, ferroelectric, and ferromagnetic properties. Finally, flexible ferroelectric photovoltaic devices are patterned based on those BiFeO3 membranes, and they have open circuit voltage and short circuit current density up to −0.25 ± 0.03 V and 0.82 ± 0.09 µA cm−2, respectively. [ABSTRACT FROM AUTHOR]

The scalable and low-cost room temperature (RT) synthesis for pure-iodine all-inorganic perovskite colloidal quantum dots (QDs) is a challenge due to the phase transition induced by thermal unequilibrium. Here, we introduce a direct RT strongly confined spontaneous crystallization strategy in a Cs-deficient reaction system without polar solvents for synthesizing stable pure-iodine all-inorganic tin-lead (Sn-Pb) alloyed perovskite colloidal QDs, which exhibit bright yellow luminescence. By tuning the ratio of Cs/Pb precursors, the size confinement effect and optical band gap of the resultant CsSnxPb1-xI3 perovskite QDs can be well controlled. This strongly confined RT approach is universal for wider bandgap bromine- and chlorine-based all-inorganic and iodine-based hybrid perovskite QDs. The alloyed CsSn0.09Pb0.91I3 QDs show superior yellow emission properties with prolonged carrier lifetime and significantly increased colloidal stability compared to the pristine CsPbI3 QDs, which is enabled by strong size confinement, Sn2+ passivation and enhanced formation energy. These findings provide a RT size-stabilized synthesis pathway to achieve high-performance pure-iodine all-inorganic Sn-Pb mixed perovskite colloidal QDs for optoelectronic applications. Photoactive pure-iodine all-inorganic colloidal perovskite quantum dots (QDs) are attractive for optoelectronic applications, however their synthesis at room temperature is challenging. Here the authors report a room temperature strongly confined strategy to synthesize CsSnxPb1-xI3 QDs. [ABSTRACT FROM AUTHOR]

Integration of magnetic materials into bio‐integrated flexible electronics will bring multi‐functionality, such as magnetoception and wireless communication. In practical application, the performance of magnetic materials and devices should remain stable during cyclic bending–unbending and they can be degradable within a designated lifetime. However, direct integration of magnetic materials with flexible and biocompatible materials and maintaining mechanically stable microwave performance have not been achieved yet. Here, ultrathin (5–50 nm) permalloy (NiFe) films deposited on biocompatible silk fibroin (SF) films are shown to be bending stable, and dissolvable. The ferromagnetic properties of NiFe films deposited on SF, Kapton, and silicon are studied and compared by ferromagnetic resonance. Benefiting from the low surface roughness of fibroin, which is only ≈0.8 nm, SF/NiFe films exhibit comparable ferromagnetic properties to Si/NiFe, better than that of Kapton/NiFe films. Moreover, the ferromagnetic resonance field of SF/NiFe films remains highly stable during cyclic bending that is exposed to both compressive and tensile strain/stress, and its temperature stability is very close to that of Si/NiFe. Finally, the whole SF/NiFe films are demonstrated to be dissolvable and biocompatible. Therefore, SF/NiFe films can be a useful and stable platform for flexible and biocompatible microwave applications. [ABSTRACT FROM AUTHOR]

MnZn ferrites that exhibit low core losses at high frequencies are suitable for the integration and miniaturization of power conversion devices. To obtain low core losses at high frequencies, it is important to understand the underlying mechanism. In this work, MnZn ferrites with various grain sizes were produced by changing the sintering temperature. The relationship between domain morphology, dynamic magnetization behavior, and core losses at high frequencies was carefully investigated. As the average grain size approached the critical size of single‐domain state, the contribution of domain wall displacement to complex permeability decreased, while domain wall resonant frequency improved significantly, resulting in the suppression of residual loss at 3 MHz. As the average grain size increased, the domain morphology changed from a single‐domain state to a multidomain state, which increased the initial permeability and decreased hysteresis loss. However, the number of domain walls increased, causing a significant decrease in the domain wall resonant frequency, and resulting in a sharp increase in residual loss. These results provide valuable insights into reducing high‐frequency core losses in MnZn ferrites by domain engineering. [ABSTRACT FROM AUTHOR]

Unidirectional magnetic anisotropy induced by exchange bias (EB) between ferromagnetic and antiferromagnetic layers is of paramount importance in various spintronic devices. Traditional setting and optimization of EB involve cooling through the Néel temperature of the antiferromagnets under biasing field in vacuum furnace which takes hours of time and cannot realize localized control of EB. Herein, an alternative process to configure EB by injection of microsecond current impulse for locally heating of the heterostructure is reported. 180‐degree exchange bias switching has been realized in both anisotropic magnetoresistance and giant magnetoresistance units, resulting in tunable magnetic field sensing functionalities. This mechanism for pinpoint control of EB provides more freedom for the design and optimization of various sensing and logic spintronics. [ABSTRACT FROM AUTHOR]

The micro-discharge effect is a failure mechanism that often appeared in space microwave devices under vacuum conditions, such as RF (radio frequency) cavity, RF satellite missile, and antenna launching communication system. How to control micro-discharge effectively and simply has become a research hotspot. In this paper, we have prepared a series of doping silver (Ag)/carbon (C) composite films by double target magnetron sputtering technology and have significantly reduced the maximum secondary electron emission coefficient (δmax) from 2.522 to 1.04 when the doping ratio of Ag/C is 1.345. Theoretically, the continuous increase of sp2 hybrid bond content tuned by the existing Ag nanoparticles has a greater contribution to the conductivity and inhibition of secondary electron emission in the Ag/C composite films. Meanwhile, the gradually emerged "multi-trap" surface structure with the increase of Ag doping content has further increased the collision between excited secondary electrons and free electrons, achieving an obvious inhibition effect. The results demonstrate that secondary electron emission can be suppressed effectively by tuning the structural feature of two kinds of compounded materials with low δmax. It is of great significance in physical mechanism analysis and design of the new doping process. [ABSTRACT FROM AUTHOR]

The domain structure fundamentally determines the piezoelectric/ferroelectric performance of ferroelectric materials. To understand the correlation between macro-properties and microstructure, the evolution of domain structure should be clearly figured out. Here, the diffraction-plane-transformation (DPT) model is proposed for the domain evaluation in BS-PT piezoelectric ceramics of rhombohedral crystalline structure. The transformation between different crystal planes is accurately revealed by the DPT model. Then, non-180° domain reversal in rhombohedral 0.4BiScO3–0.6PbTiO3 piezoelectric ceramics (abbreviated as BS-PT) can be quantitatively estimated, whether in electric poling or thermal depoling processes. Experimentally, the correlations between piezoelectric coefficients, electromechanical coupling properties, and non-180° domain reversal percentage are investigated. It is proven that the DPT model provides an effective method for the non-180° domain estimation in rhombohedral crystalline ceramics. [ABSTRACT FROM AUTHOR]

Highlights: The (001)-oriented ferromagnetic La0.67Sr0.33MnO3 films are stuck onto the (011)-oriented ferroelectric single-crystal 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 substrate with 0° and 45° twist angle. By applying a 7.2 kV cm−1 electric field, the coexistence of uniaxial and fourfold in-plane magnetic anisotropy is observed in 45° Sample, while a typical uniaxial anisotropy is found in 0° Sample. Manipulating strain mode and degree that can be applied to epitaxial complex oxide thin films have been a cornerstone of strain engineering. In recent years, lift-off and transfer technology of the epitaxial oxide thin films have been developed that enabled the integration of heterostructures without the limitation of material types and crystal orientations. Moreover, twisted integration would provide a more interesting strategy in artificial magnetoelectric heterostructures. A specific twist angle between the ferroelectric and ferromagnetic oxide layers corresponds to the distinct strain regulation modes in the magnetoelectric coupling process, which could provide some insight in to the physical phenomena. In this work, the La0.67Sr0.33MnO3 (001)/0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (011) (LSMO/PMN-PT) heterostructures with 45º and 0º twist angles were assembled via water-etching and transfer process. The transferred LSMO films exhibit a fourfold magnetic anisotropy with easy axis along LSMO < 110 >. A coexistence of uniaxial and fourfold magnetic anisotropy with LSMO [110] easy axis is observed for the 45° Sample by applying a 7.2 kV cm−1 electrical field, significantly different from a uniaxial anisotropy with LSMO [100] easy axis for the 0° Sample. The fitting of the ferromagnetic resonance field reveals that the strain coupling generated by the 45° twist angle causes different lattice distortion of LSMO, thereby enhancing both the fourfold and uniaxial anisotropy. This work confirms the twisting degrees of freedom for magnetoelectric coupling and opens opportunities for fabricating artificial magnetoelectric heterostructures. [ABSTRACT FROM AUTHOR]

The electron‐phonon interaction is known as one of the major mechanisms determining electrical and thermal properties. In particular, it alters the carrier transport behaviors and sets fundamental limits to carrier mobility. Establishing how electrons interact with phonons and the resulting impact on the carrier transport property is significant for the development of high‐efficiency electronic devices. Here, carrier transport behavior mediated by the electron‐phonon coupling in BiFeO3 epitaxial thin films is directly observed. Acoustic phonons are generated by the inverse piezoelectric effect and coupled with photocarriers. Via the electron‐phonon coupling, doughnut shape carrier distribution has been observed due to the coupling between hot carriers and phonons. The hot carrier quasi‐ballistic transport length can reach 340 nm within 1 ps. The results suggest an effective approach to investigating the effects of electron‐phonon interactions with temporal and spatial resolutions, which is of great importance for designing and improving electronic devices. [ABSTRACT FROM AUTHOR]

To achieve compact and lightweight power conversion devices, magnetic core materials such as MnZn ferrite are highly desired with low core losses at high frequencies above megahertz. In this work, high-valent Sn4+ ions were doped into MnZn ferrite to manipulate the electromagnetic properties and suppress the high-frequency core losses. The distribution of Sn4+ in MnZn ferrite was investigated by transmission electron microscopy with energy dispersive x-ray analysis, which indicated that most of the substituted Sn4+ ions remained at the grain boundaries rather than dissolving into the lattice, and thus greatly impacted the electromagnetic properties of MnZn ferrite. The initial permeability and saturation induction decreased monotonically with the Sn substitution. The core loss was reduced to 457 kW m−3 at 3 MHz, 30 mT, and 25 °C when the Sn substitution content was 0.003, due to the effective suppression of eddy current loss and residual loss. The sample with a Sn content of 0.003 exhibited excellent overall electromagnetic properties, which could be potentially useful in high-frequency transformers, converters, and power sources. [ABSTRACT FROM AUTHOR]

Memristors are of great significance for the construction of memory devices and neuromorphological computing, which need a fast response time for ultrahigh data storage, ultrafast information processing, and efficient neuromorphic computing. Currently, memristors based on perovskite oxide materials generally have a long response time. In this paper, the electroforming‐free memristive behavior based on Ar+ irradiating induced oxygen vacancy modulation in SrTiO3 (STO) has been investigated. The Ag/STO/(Ta/Pt) device shows a stable bipolar resistive switching (RS) characteristic and can realize ultrafast multi‐resistance switching behavior. More importantly, its conductance can be continuously controlled with short pulse on the nanosecond scale to simulate potentiation and depression of synapse, promising potential application in ultra‐fast biological synapse and high‐efficiency training of neural networks. More importantly, the defect engineering strategy used in this work provides more freedom for the design and optimization of versatile memristor devices. [ABSTRACT FROM AUTHOR]

Nano-FeS has great potential for use in the management of radioactive contaminants. In this paper, we prepared a FeS@Stenotrophomonas sp. composite material by ultrasonic chemistry, and it showed excellent removal of uranium and thorium from the solution. Through optimization of the experimental conditions, it was found that the maximum adsorption capacities for uranium and thorium reached 481.9 and 407.5 mg/g for a composite made with a synthetic ratio of 1:1, pH 5 and 3.5, respectively, for U and Th, and sonication for 20 min. Compared with those of FeS or Stenotrophomonas alone, the removal capacity was greatly improved. The results of a mechanistic study indicated that efficient removal of the uranium and thorium was due to ion exchange, reduction, and microbial surface adsorption. FeS@Stenotrophomonas sp. could be applied to U(VI) and Th(IV) extraction for radioactive water. [ABSTRACT FROM AUTHOR]

The emerging market of wearable devices for tracking and positioning requires the development of highly flexible magnetic sensors. Due to the stable magnetoresistance ratio and simple fabrication process, sensors based on the anisotropic magnetoresistance (AMR) effect have been proposed as promising candidates. However, the stability of AMR sensors under different bending situations has rarely been investigated. In this work, we proposed a flexible AMR magnetic sensor deposited on an ultra-thin Kapton substrate, which exhibits excellent anti-fatigue behavior at different bending curvatures ranging from 1/3 to 1/10 mm−1. Experimental results show that the sensitivity of our proposed flexible AMR sensor remains as high as 0.25 Oe−1 after being bent 500 times, showing promising potential for application in wearable electronic devices. [ABSTRACT FROM AUTHOR]